Air-on-oil pistons are well known and are used as servo-motors, intensifiers, and similar devices where air pressure can be maintained at constant high pressures to do work while movement of the oil or hydraulic fluid needed to apply the pressure can be accomplished at nominal or minimal pressure and work force. Typical of such a device is that disclosed by C. H. T. Woodward in U.S. Pat. No. 3,464,317 where each cylinder of a simple double-ended cylinder piston is available to provide the push-pull action needed for reciprocating motion.
The use of double-ended cylinders with similar air-on-oil arrangements in intensifiers has been published in Plant Engineering for Sept. 18, 1975 at p. 149-151 by Gene Swatty entitled "Increasing Fluid Pressure with Hydraulic Intensifiers".